Flash memory controller

ABSTRACT

Methods, systems and computer program products for implementing a polling process among one or more flash memory devices are described. In some implementations, the polling process may include sending a read status command to a flash memory device to detect the ready or busy state of the flash memory device. A status register may be included in the flash memory device for storing a status signal indicating an execution state of a write (or erase) operation. A solid state drive system may perform the polling process by reading the status register of the flash memory device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 60/976,616 titled “SSD CONTROLLER INVENTION #1,” filed on Oct. 1,2007, and U.S. Provisional Application Ser. No. 60/976,624 titled “SSDCONTROLLER INVENTION #2,” filed on Oct. 1, 2007, the disclosure of eachof which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The subject matter of this application is generally related to memorydevices.

BACKGROUND

Many electronic devices include embedded systems with central processorunits (CPUs) to control the operation of the devices providing greatlyenhanced functionality and operational flexibility. Typically,non-volatile memory is included as a portion of the embedded system tostore operating system program code and data for operating the embeddedsystem. Recently, embedded systems have begun to use flash memory forthe non-volatile memory. Flash memory may advantageously be reprogrammedwhile also providing non-volatile storage of information.

SUMMARY

Methods, systems and computer program products for implementing apolling process among one or more flash memory devices are described. Insome implementations, the polling process may include sending a readstatus command to a flash memory device to detect the ready or busystate of the flash memory device. A status register may be included inthe flash memory device for storing a status signal indicating anexecution state of a write (or erase) operation. A solid state drivesystem may perform the polling process by reading the status register ofthe flash memory device.

In some implementation, a method is described that includes asserting acontrol signal to one or more devices, determining an initial wait timeafter asserting the control signal, issuing a first command based on theinitial wait time, determining a first interval time associated with thefirst command and a second command, and issuing the second command basedon the first interval time.

In some implementation, a method is described that includes controllinga plurality of memory devices including a first group of memory devicesand a second group of memory devices, determining a first periodassociated with the first group of memory devices, issuing a firstcommand to the first group of memory devices based on the first period,determining a second period associated with the second group of memorydevices, and issuing a second command to the second group of memorydevices based on the second period.

In some implementation, a device is described that includes a firstprogrammable timer to specify an initial wait time associated withissuing one or more commands to at least one device, and a secondprogrammable timer to specify an interval time to control a periodbetween each issued command

In some implementation, a device is described that includes a bus toreceive one or more commands to one or more memory devices and tocontrol the one or more memory devices based on the issued commands, anda memory controller to perform data polling while the issued commandsare being processed by the one or more memory devices

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a block diagram of an example memory array.

FIG. 2A shows a timing diagram associated with each pin in an exampleNAND flash interface during a data read operation.

FIG. 2B shows an example timing diagram associated with each pin in aNAND flash interface during a data program operation.

FIG. 2C shows an example timing diagram associated with each pin in aNAND flash interface during a block erase operation.

FIG. 3 shows an example solid state drive.

FIG. 4 shows an example initial wait time with respect to a read/busyoutput signal “R/B_” of a flash memory device.

FIG. 5 shows an example process for issuing one or more read statuscommands.

FIG. 6 shows an example process for status polling based on a writecycle time and a read cycle time.

FIGS. 7-12 show various example electronic systems implementing a harddisk drive system.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION Flash Memory Overview

The use of memory devices, such as flash electrically erasableprogrammable read only memory (EEPROM), is becoming more widespread. Forexample, jump drives, memory cards, and other nonvolatile memoryappliances are commonplace in cameras, video games, computers, and otherelectronic devices. FIG. 1 shows a block diagram of a memory array 100.

As shown in FIG. 1, a memory array 100 may be organized in bits. Forexample, the memory array 100 may include 8-bit depth 108. The memoryarray 100 also may be organized in bytes. For example, the memory array100 may include a portion 104 containing 2 k bytes, and a portion 106containing 64 bytes. The memory array 100 further may be organized intopages. For example, the memory array 100 may include 512K pages 102. Asingle page 112 may be organized into two portions: a first portion 114(e.g., portion 104 representing 2 k bytes), and a second portion 116(e.g., a portion 106 representing 64 bytes). The second portion 116 maygenerally correspond to an eight-bit wide data input/output (I/O) path(e.g., I/O [0]-I/O [7]). Even further, the memory array 100 may bearranged in blocks. For example, the memory array 100 may include ablock 110, which equates to 64 pages. In all, an 8-Mb memory device maybe formed using the foregoing bits, bytes, pages and blocks.

The memory array shown in FIG. 1 may be configured as a flash memory. Insome implementations, the flash memory may be a “NAND” type flashmemory. NAND flash memory generally has faster erase and write times,higher density, lower cost per bit, and more endurance than NOR-typeflash memory. NAND flash memory may be coupled with a NAND flash I/Ointerface. The NAND flash I/O interface, however, typically allows onlysequential access to data. Of course, the memory array shown in FIG. 1also may be of the form of any one of a NOR Flash EEPROM, AND FlashEEPROM, DiNOR Flash EEPROM, Serial Flash EEPROM, DRAM, SRAM, ROM, EPROM,FRAM, MRAM, or PCRAM.

A NAND flash I/O interface may include multiple pins each correspondingto a specific function. An example interface is shown in Table 1.

TABLE 1 PIN PIN Function I/O [7:0] Data in/out CLE Command latch enableALE Address latch enable CE_(—) Chip enable RE_(—) Read enable WE_(—)Write enable WP_(—) Write protect R/B_(—) Read/busy output

As shown in TABLE 1 above, various pin functions may correspond todesignated pins in the interface.

Exemplary Timing Diagram for Data Read Operation

FIG. 2A shows an example timing diagram associated with each pin in aNAND flash interface during a data read operation. Referring to FIG. 2A,region 202 may represent a period during which one or more commands arebeing sent to a flash memory device, while region 204 may represent aperiod during which data are being transferred to/from the flash memorydevice. As shown, the write enable signal “WE_” may be pulsed (e.g., ata 25-ns period) to allow row address (e.g., RA 1, RA 2, and RA 3) andcolumn address (e.g., CA 1 and CA 2) information to be latched in theNAND flash memory device. Command “00 h” appearing on the data in/outI/O [7:0] pin may indicate a read address input, while command “30 h”may indicate a read start.

Other commands also may be used. For example, other memory commands mayinclude, but are not limited to read operations, write operations, eraseoperations, read status operations, read ID operations, writeconfiguration register operations, write address operations, and resetoperations. As an example, command “05 h” may represent a random dataread command; command “10 h” may represent a page program command;command “20 h” may represent a chip erase command; command “21 h” mayrepresent a sector erase command; command “30 h” may represent a readstart command; command “35 h” may represent a page read for copycommand; command “39 h” may represent a write device address command;command “60 h” may represent a block erase command; command “70 h” mayrepresent a read status command; command “80 h” may represent a serialdata input (writer to buffer) command; command “85 h” may represent arandom data input command; command “8Fh” may represent a target addressinput for copy command; command “90 h” may represent a read device typecommand; command “AOh” may represent a write configuration registercommand; command “COh” may represent a program/erase suspend command;and command “DOh” may represent a program/erase command; and command“FFh” may represent a reset command, to name a few examples.

An example of row and column address multiplexing on the data in/outpins (e.g., I/O[7:0]) may be as shown below in TABLE 2.

TABLE 2 CYCLE I/O [0] I/O [1] I/O [2] I/O [3] I/O [4] I/O [5] I/O [6]I/O [7] 1^(st) Cycle: A0 A1 A2 A3 A4 A5 A6 A7 Column Address 2^(nd)Cycle: A8 A9 A10 A11 L L L L Column Address 3^(rd) Cycle: A12 A13 A14A15 A16 A17 A18 A19 Column Address 4^(th) Cycle: A20 A21 A22 A23 A24 A25A26 A27 Column Address 5^(th) Cycle: A28 A29 A29 L L L L L ColumnAddress

In some implementations, higher address bits may be utilized foraddressing larger memory arrangements (e.g., A30 for 2 Gb, A31 for 4 Gb,A32 for 8 Gb, A33 for 16 Gb, A34 for 32 Gb, A35 for 64 Gb and the like).

Meanwhile, with read enable signal “RE_” pulsing, data such as D_(out)N,D_(out)N+1, D_(out)N+2 . . . . D_(out)M may be read from the NAND flashmemory device. The read/busy output signal “R/B_” in a particular logicstate may indicate whether the output is busy. For example, theread/busy output signal “R/B_” in a low logic state may indicate a busystate at the output. In this example, the read/busy output signal “R/B_”may go logic high (i.e., become logic high which indicates a readystate) some period of time after the last rising edge of write enablesignal “WE_”.

As shown, the “tR” period, which indicates a data transfer time for datato transfer from a cell to an internal page buffer, may span from theread start command “30 h” to the rising edge of the ready/busy outputsignal “R/B_” and indicates a reading time for reading data. In someimplementations, the “tR” period may determine the performance of asolid state drive system (e.g., solid state drive system 300 shown inFIG. 3) for READ operation. In some implementations, a long “tR” periodmay impose a longer wait time for a solid state controller (e.g., solidstate controller 308) before the READ data may be available to thecontroller.

Before the data becomes ready, the NAND flash I/O interface may be idleand consume unnecessary bandwidth. Thus, it may be desirable toconstantly maintain the NAND flash I/O interface in a busy state toachieve bandwidth. For example, if the NAND flash I/O interface isrunning at tRC=25 ns, the upper limit of an achievable bandwidth may be40 MB/s (e.g., based on an assumption that a 8-bit data bus is used, andthat the NAND flash memory has unlimited bandwidth such that data maycontinuously be sent from the NAND flash memory to the solid statecontroller). However, this objective may be difficult to achieve giventhe “tR” period to read a page from a memory cell in a NAND flash memoryto an internal buffer before returning the read data to the solid statecontroller.

Thus, in some implementations, multiple devices (e.g., multiple chipenable signals) may be bundled into a single channel while sharing asame NAND flash I/O interface such that the “tR” time may be covered asmuch as possible while allowing data to be available from at least onedevice of the same channel.

In some implementations, the data transfer time may be in the range ofabout 25 μs for a single level cell (SLC) device or in the range ofabout 60 μs for a multi-level cell (MLC) device, as will be discussed ingreater detail below. During the “tR” period, the ready/busy outputsignal “R/B_” may be asserted as a logical “0”, indicating that theflash memory is in a busy state, during which data, for example, may notbe written or erase.

Single Level Cell and Multi-Level Cell Devices Overview

Each cell in a memory device can be programmed as a single bit per cell(i.e., single level cell—SLC) or multiple bits per cell (i.e., multiplelevel cell—MLC). Each cell's threshold voltage generally determines thetype of data that is stored in the cell. For example, in a SLC memorydevice, a threshold voltage of 0.5V may indicate a programmed cell(i.e., logic “0” state) while a threshold voltage of −0.5V may indicatean erased cell (i.e., logic “1” state).

As the performance and complexity of electronic systems increase, therequirement for additional memory in a system also increases. However,in order to continue to reduce the costs of the system, the parts counttypically must be kept to a minimum. In a memory application, this canbe accomplished by increasing the memory density of an integratedcircuit. Specifically, memory density can be increased by using MLCmemory devices. MLC memory devices can increase the amount of datastored in an integrated circuit without adding additional cells and/orincreasing the size of the die. MLC memory devices can store two or moredata bits in each memory cell. However, MLC memory devices require tightcontrol of the threshold voltages in order to use multiple thresholdlevels per cell. One problem with non-volatile memory cells that areclosely spaced, and MLC in particular, is the floating gate-to-floatinggate capacitive coupling that causes interference between cells. Theinterference can shift the threshold voltage of neighboring cells as onecell is programmed.

MLC memory devices also have a lower reliability than SLC memory devicesdue, in part, to the increased quantity of states requiring more closelyspaced threshold voltages. For example, a bad bit in a memory deviceused to store photographs can be tolerated more easily than a bad bit ina memory device that stores code. A bad bit in a photograph might onlyproduce a bad pixel out of millions of pixels while a bad bit in code orother data could mean a corrupted instruction that affects the operationof an entire program.

A MLC memory device has two or more threshold voltage distributions, andhas two or more data storage states corresponding to the voltagedistributions. For example, a MLC memory device that can program 2-bitdata has four data storage states (e.g., [11], [10], [01] and [00]).These states may correspond to the threshold voltage distributions ofthe MLC memory device. For example, assuming that the respectivethreshold voltage distributions of the memory cell are −2.7 V or less,0.3 V to 0.7 V, 1.3 V to 1.7 V, and 2.3 V to 2.7 V, the states [11],[10], [01] and [00] correspond to −2.7 V or less, 0.3 V to 0.5 V, 1.3 Vto 1.7 V, and 2.3 V to 2.7 V, respectively.

A reading operation of the flash memory device with multi-level cellsmay be carried out by detecting data of a multi-level cell. Detectioncan include, for example, determining a difference between cell currentsflowing through a selected memory cell according to a constant amount ofbit line current and a word line voltage of a step-shaped waveform.

A programming operation of the flash memory device with multi-level cellmay be carried out by applying a predetermined program voltage to thegate of the selected memory cell and then applying a ground voltage tothe bit line. A power supply voltage may then be applied to the bit linein order to prevent the programming. If the program voltage and theground voltage are respectively applied to the word line and the bitline of the selected memory cell, a relatively high electric field isapplied between a floating gate and a channel of the memory cell. Due tothe electric field, electrons of the channel pass through an oxide layerformed between the floating gate and the channel, so that a tunnelingoccurs therein. In this manner, a threshold voltage of the memory cellprogrammed by an accumulation of the electrons in the floating gate maybe increased.

Exemplary Timing Diagram for Data Page Operation

FIG. 2B shows an example timing diagram associated with each pin in aNAND flash interface during a data program operation. Referring to FIG.2B, region 206 may represent a period during which one or more commandsmay be sent to a flash memory device, while region 208 may represent aperiod during which programming data may be sent to the flash memorydevice, and region 210 may represent a period during which a statuscheck may be sent to the flash memory device for checking status of thememory device.

As shown, command “80 h” appearing on the data in/out I/O [7:0] pin mayindicate serial data input (e.g., D_(in)N . . . D_(in)M). Command “10 h”may indicate an auto program, followed by a status read as indicated bycommand “70 h”. I/O[0]=“0” may indicate an no-error condition, whileI/O[0]=“1” may indicate that an error in auto programming has occurred.

Also, as already discussed, the ready/busy output signal “R/B_” may belogic low, indicating a busy state. In some implementations, theduration of the low logic state of the ready/busy output signal “R/B_”may range in the order of hundreds of μs. Also, a rising edge of theread enable signal “RE_” can trail a rising edge of the write enablesignal “WE_” by a period of time. In some implementations, this periodof time may be in the range of about 60 ns.

Also, as shown in FIG. 2B, the timing period “tPRG”, which spans fromthe trailing edge to the rising edge of the ready/busy output signal“R/B_”, may indicate a program time for programming data. In someimplementations, the program time “tPRG” may be in the range of about200 μs to about 700 μs for a SLC device or in the range of about 800 μsto about 3 ms for a MLC device.

In some implementations, the program time “tPRG” may be similar to the“tR” period but for programming data as opposed to reading data. Duringthe “tPRG” period, the ready/busy output signal “R/B_” may be assertedas a logical “0”, indicating that the flash memory is in a busy state,during which data, for example, may not be read or erase.

Exemplary Timing Diagram for Block Erase Operation

FIG. 2C shows an example timing diagram associated with each pin in aNAND flash interface during a block erase operation. Referring to FIG.2C, region 212 may represent a period during which one or more commandsmay be sent to a flash memory device, while region 214 may represent aperiod during which a status check may be sent to the flash memorydevice for checking status of the memory device.

As shown, command “60 h” appearing on the data in/out I/O [7:0] pin mayindicate a block erase operation, with sequential row addresses (e.g.,RA 1, RA 2, and RA 3) being supplied. Command “DOh” may indicate a cycle2 block erase operation. The block erase operation may be checked by astatus read (command “70 h”), where I/O[0]=“0” may indicate an no-errorcondition, while I/O[0]=“1” may indicate that an error in block erasehas occurred.

In this example, the ready/busy output signal “R/B_” may be logic lowfor a period of time such as in the range of about a millisecond (e.g.,with a predetermined maximum). Similarly, a rising edge of the readenable signal “RE_” may trail a rising edge of the write enable signal“WE_”. As another example, a rising edge of the write enable signal“WE_” corresponding to the “DOh” command and/or a falling edge of theready/busy output signal “R/B_” may be in the range of about 100 ns.

Also, as shown in FIG. 2C, the timing period “tBERS”, which spans fromthe trailing edge to the rising edge of the ready/busy output signal“R/B_”, may indicate a block erase time for erasing block data.

In some cases, a block erase operation may not need to access the NANDflash I/O interface other than sending one or more block erase commands(or reading status commands if not using read a ready/busy output signal“R/B_”). The performance of a solid state drive system may rely on theblock erase operation indirectly. In certain cases, at the verybeginning of a block erase operation, the drive may determine that anumber of erased pages are available for data programming. As a result,the drive may maintain a programming operation without the need ofperforming a block erase operation. However, as the data stored in thedrive is modified along with the operation of the drive, less pagesbecome available for data programming such that the drive would need toperform one or more block erase operations to vacant empty page(s) fordata programming. Thus, a long “tBERS” period would yield a longer waitperiod for the solid state drive system to honor the PROGRAM commands.In other words, the impact of a block erase operation on the overalldrive performance depends heavily on the garbage collection mechanismhandled by the firmware (e.g., firmware 324).

In some implementations, the block erase time “tBERS” may be in therange of about 1.5 ms to about 2 ms for a SLC device or in the range ofabout 1.5 ms to about 10 ms for a MLC device. During the “tBERS” period,the ready/busy output signal “R/B_” may be asserted as a logical “0”,indicating that the flash memory is in a busy state, during which data,for example, may not be read or written.

Solid State Drive

FIG. 3 shows an example solid state drive system 300. As shown in FIG.3, the system 300 includes a host 302 and a solid state drive 304. Thesolid state drive 304 may include a host interface 310, centralprocessor unit (CPU) 323, a memory controller interface 328, a memorycontroller 330 and one or more flash memory devices 306 a-306 d.

The host 302 may communicate with the solid state drive 304 through thehost interface 310. The host interface 310, in some implementations, mayinclude a Serial Advanced Technology Attachment (SATA) interface or aParallel Advanced Technology Attachment (PATA) interface. A SATAinterface or PATA interface may be used to convert serial or paralleldata into parallel or serial data, respectively. For example, if thehost interface 310 includes a SATA interface, then the SATA interfacemay receive serial data transferred from the host 302 through a bus 303(e.g., a SATA bus), and convert the received serial data into paralleldata. In other implementations, the host interface 310 may include ahybrid interface. In these implementations, the hybrid interface may beused in conjunction with, for example, a serial interface.

The host interface 310, in some implementations, may include one or moreregisters in which operating commands and addresses from the host 302may be temporarily stored. The host interface 310 may communicate awrite or read operation to a solid state controller 308 in response tothe stored information in the register(s).

In some implementations, the solid state drive 304 may include one ormore channels 326 a-326 d (e.g., four or eight channels), and eachchannel may be configured to receive one or more control signals (e.g.,four chip enable signals) from the host 302 or from the flash memories306 a-306 d.

Flash Memory Device

Each flash memory device 306, in some implementations, may include anonvolatile memory (e.g., a single-level flash memory or a multi-levelflash memory). In some implementations, the nonvolatile memory mayinclude a NAND-type flash memory module. A NAND-type flash memory modulemay include a command/address/data multiplexed interface such thatcommands, data, and addresses may be provided through correspondinginput/output pins. Advantages of using NAND-type flash memory, asopposed to a hard disk approach, include: (i) faster boot and resumetimes; (ii) longer battery life (e.g., for wireless applications); and(iii) higher data reliability.

In some implementations, each flash memory device may be connected to achannel 326. Each channel may support, for example, one or more inputand output lines, chip select signal lines, chip enable signal lines andthe like. The channel also may support other signal lines such as writeenable, read enable, read/busy output, and reset signal lines. In someimplementations, the flash memory devices 306 a-306 d may share a commonchannel. In other implementations, to increase the degree ofparallelism, each flash memory device may have its own channel connectedto the solid state drive 304. For example, flash memory device 306 a maybe connected to the solid state drive 304 using channel 326 a; flashmemory device 306 b may be connected to the solid state drive 304 usingchannel 326 b; flash memory device 306 c may be connected to the solidstate drive 304 using channel 326 c; and flash memory device 306 d maybe connected to the solid state drive 304 using channel 326 d.

In some implementations, the flash memory devices 306 a-306 d may bedetachable. In some implementations, the flash memory devices 306 a-306d may be connected to the solid state drive 304 using standardconnectors. Examples of standard connectors may include, withoutlimitation, SATA, USB (Universal Serial Bus), SCSI (Small ComputerSystem Interface), PCMCIA (Personal Computer Memory Card InternationalAssociation), and IEEE-1394 (Firewire).

In some implementations, each flash memory device 306 may include one ormore solid state storage elements arranged in a bank. A solid statestorage element may be partitioned into pages. In some implementations,a solid state storage element may have a capacity of 2000 bytes (i.e.,one page). A solid state storage element, in some implementations, mayinclude two registers to provide a total capacity of 4000 bytes (i.e., 4kB).

In some implementations, each flash memory device 306 also may includeone or more banks each being selected using a chip enable signal or chipselect signal. The chip enable or chip select signal may select one ormore solid state storage elements in response to a host command.

In some implementations, each solid state storage element may includeone or more single-level cell (“SLC”) devices. In some implementations,each sold state storage element may include one or more multi-level cell(“MLC”) devices. The SLC or MLC devices may be selected using a chipenable signal or chip select signal, which may be generated by the solidstate controller 308 using a combination of control and addressinformation received from the host 302.

Where multiple banks are used, in some implementations, the solid statedrive 304 may access more than one bank in a same flash memory device atthe same time. In some implementations, the solid state drive 304 mayaccess different banks in different flash memory devices at the sametime. The capability to access more than one bank allows the solid statedrive 304 to fully utilize the available resources and channels 326a-326 d to increase the overall performance of the solid state drive304. Furthermore, where the flash memory devices 306 a-306 d share asame memory input/output line and control signal (e.g., chip enablesignal), the number of pins of the solid state controller 308 may bereduced to further minimize the cost for manufacturing the solid statedrive 304.

Solid State Controller

The solid state controller 308 may receive one or more service requestsor commands (e.g., read and program requests). The solid statecontroller 308 may be configured to handle any command, status, orcontrol request for access to the flash memory devices 306 a-306 d. Forexample, the solid state controller 308 may be configured to manage andcontrol storage and retrieval of data in the flash memory devices 306a-306 d.

In some implementations, the solid state controller 308 may be a part ofa microcomputer system under the control of a microprocessor (notshown). The solid state controller 308 may control the flow of commandsand data between the host 302 and the solid state drive 304. In someimplementations, the solid state controller 308 may include read-onlymemory (ROM), random-access memory (RAM) and other internal circuits.The solid state controller 308, in some implementations, may beconfigured to support various functions associated with the flash memorydevices 306 a-306 d, such as, without limitation, diagnosing the flashmemory devices 306 a-306 d, sending commands (e.g., activation, read,program, erase, pre-charge and refresh commands) to the flash memorydevices 306 a-306 d, and receiving status from the flash memory devices306 a-306 d. The solid state controller 308 may be formed on a differentchip as the flash memory devices 306 a-306 d (e.g., formed on a samechip as the solid state drive 304) or on a same chip. The flash memorydevices 306 a-306 d may be coupled with the memory interface 328. Insome implementations, if the flash memory devices 306 a-306 d includeNAND-type memory devices, the memory interface 328 may be a NAND flashinput/output interface.

As shown in FIG. 3, the solid state controller 308 may include an errorchecking code module 312, interface logic 314, a sequencer 316 and aformatter 318. In some implementations, the solid state controller 308may be coupled with the CPU 323 including embedded firmware 324 by whichthe solid state controller 308 may be controlled. The CPU 323 mayinclude a microprocessor, a signal processor (e.g., a digital signalprocessor) or microcontroller. In some implementations, the CPU 323 withthe embedded firmware 324 may reside outside of the solid state drive304.

In some implementations, the solid state drive 304 (and/or the host 302)may be mounted on a system on-chip (SOC). The SOC, in theseimplementations, may be fabricated using, for example, a digitalprocess. The SOC may include an embedded process system (e.g., anembedded CPU) separate from that in the solid state drive 304. The SOCalso may include a SRAM, system logic, cache memory and cache controllerfor processing program code and data. The program code and dataassociated with the embedded process system may be stored in the flashdevices 306 a-306 d, and communicated to the SOC through, for example,an SOC interface. The SOC interface may be used by a translator fortranslating information flowing between the interface and the internalbus structure of the SOC. Control signals may flow from the SOC to theflash devices 306 a-306 d while instructions and data may flow from theflash device 308 to the SOC during read operations. Instructions anddata also may flow towards the flash devices 306 a-306 d such as whenthe main memory in the flash devices 306 a-306 d are in WRITEoperations.

In some implementations, the flash devices 306 a-306 d may be controlledby the memory controller 330. The host 302 may communicate with theflash devices 306 a-306 d through the memory interface 328 coupled withthe memory controller 330. In some implementation, the memory interface328 may be a NAND flash interface.

The memory controller 330 may be connected to the flash memory devices306 a-306 d through a corresponding pin or terminal. In theseimplementations, the memory controller 330 may be implemented as anapplication specific integrated circuit (ASIC) or a system on a chip(SOC). In addition, signal CNFG may connect through circuitry on flashdevices 306 a-306 d in serial fashion.

Status Polling

As discussed above, the read/busy output signal “R/B_” in a particularlogic state may indicate whether the output is busy. For example, theread/busy output signal “R/B_” in a low logic state may indicate a busystate at the output. In this example, the read/busy output signal “R/B_”may go logic high (i.e., become logic high which indicates a readystate) some period of time after the last rising edge of write enablesignal “WE_”.

Generally, a flash memory device only has one internal write chargepump. Therefore, writing data to the flash memory device (i.e.,programming the device) puts the memory device into a busy state suchthat data cannot be read from the memory device during a writeoperation. If a read operation is performed during the busy state, alogical “00” may be returned. In this case, the busy state for a writeoperation may last several microseconds.

Similarly, initiating an erase operation of the flash memory device putsthe memory device into the busy state. The device typically enters thebusy state for 0.50-1.0 seconds during an erase operation. During thistime, the device also is not accessible.

Lack of accessibility to the flash memory device during write and eraseoperations may cause a system implementing the flash memory device tooperate slower than normal. The processor (e.g., CPU 323) or the memorycontroller 330 that is attempting to read the content of the flashmemory device must wait until the write or erase operations are completebefore being able to obtain the desired data.

Further, during this waiting period (e.g., during which write or eraseoperations are in process), the processor or the memory controller 330may use the read/busy output signal “R/B_” to detect whether the flashmemory device is in a ready condition (e.g., detect whether the flashmemory device is ready to be read). If the flash memory device is busy,a busy status may be returned to the processor or the memory controller330. If the flash memory device is idle, an idle status may be returned.

While the foregoing process to detect a ready/busy condition of theflash memory device allows the processor or the memory controller 330 toread (or write or erase) the content of the flash memory deviceimmediately after other operations (e.g., write or erase operations) arefinished, the flash memory device typically requires an additional pincount to support this process.

To avoid the need for an additional pin count, in some implementations,the processor or the memory controller 330 may utilize a polling methodby sending a read status command (e.g., a status read command “70 h”) tothe flash memory device to detect the ready or busy state (e.g., readingstatus of a command being executed, reading a busy/idle or pass/failstate of the command, and the like) of the flash memory device. In someimplementations, a status register 336 a-336 d may be connected to theflash memory device for storing a status signal indicating an executionstate of a write (or erase) operation. The processor or the memorycontroller 330 may perform a polling method by reading the statusregister 336 a-336 d of the flash memory device. In someimplementations, the flash memory device may accept the read statuscommand even if the flash memory device is in a busy state, as shownbelow in TABLE 3:

TABLE 3 I/O Page Program Block Erase Read Definition I/O [0] Pass/failPass/fail Not use Pass “0” Fail “1” I/O [1] Not use Not use Not use —I/O [2] Not use Not use Not use — I/O [3] Not use Not use Not use — I/O[4] Not use Not use Not use — I/O [5] Not use Not use Not use — I/O [6]Ready/busy Ready/busy Ready/busy Busy “0” Fail “1” I/O [7] Write protectWrite protect Write protect Protected “0” Not protected “1”

In some implementations, data polling may be set under the conditionsthat the chip enable signal (CE_) is set to a logic low while the writeenable signal (WE_) is set to a logic high. In operation, the host(e.g., host 302) or the memory controller (e.g., memory controller 330)may output a write/erase busy signal to initiate a writing/erasingoperation. The write/erase busy signal may set the status register 336a-336 d of the flash memory device to logic “1”. During this time, theCPU (e.g., CPU 323) may read the content of the flash memory devicewhile the write (or erase) operation is in progress.

While the flash memory device accepts a read status command from theprocessor or the memory controller 330, the processor or the memorycontroller 330 continues polling for detecting the completion of writingor erasing or erasure throughout writing or erasing or erasure of theflash memory device, which can overload both the flash memory device andthe processor or memory controller 330 with the polling results.

Thus, in some implementations, the memory controller 330 may include aprogrammable timer 332, and the programmable timer may be used todetermine an initial wait time before polling (i.e., before sending aread status command). More specifically, the initial wait time maydefine a time period during which the memory controller 330 may waitbefore issuing a status check to the flash memory device (e.g., during aread, program or erase operation). In some implementations, the initialwait time may be determined based on one or more factors, such as the“tR”, “tPROG” and “tBERS” parameters.

In some implementations, at the end of the initial wait time, the memorycontroller 330 may begin issuing one or more commands (e.g., read statuscommand “70 h”) to check the status of the flash memory (e.g.,ready/busy, pass/fail, etc.).

In some implementations, the memory controller also may include a secondprogrammable timer 334 that may be used for controlling the intervalbetween each command (e.g., read status commands). In someimplementations, the appropriate value for the interval may bedetermined by the system firmware (e.g., firmware 324), and such adetermination may be based on one or more parameters associated withpower and performance (e.g., because frequent polling would increaseperformance but consume more power).

In some implementations, the second programmable timer 324 may controlthe precise period between each status check or each read statuscommand. By controlling the initial wait time before issuing the readstatus command and the interval of each issued read status command, thememory controller 330 can timely detect the busy/ready condition of theflash memory.

Additionally, when a read status command is asserted, power consumptionassociated with the memory controller 330 and flash memory devices 306a-306 d in executing the command may be increased. Further, if aparticular channel is used for sending one or more READ status commands,the channel may be blocked, preventing a next command from being sent toanother device (or delaying the execution of the next command). Thus, bycontrolling the interval of each issued read status command, the numberof read status commands may be regulated. Regulating the number of readstatus command allows power associated with the memory controller 330and the flash memory devices 306 a-306 d to be conserved, which canenhance the overall power performance of the memory controller 330 andflash memory devices 306 a-306 d (or the solid state drive 308).

While the above description pertains to a read command a read statuscommand, it should be noted that one ordinary skill in the art wouldrecognize that the foregoing description also may be applied to programoperations. In these implementations, a program status command may besent and regulated based on the polling process described above.

FIG. 4 shows an example initial wait time with respect to the read/busyoutput signal “R/B_” of a flash memory device. As shown in FIG. 4, thetiming period “t3”, which spans from the trailing edge and to the risingedge of the read/busy output signal “R/B_” (e.g., during a logical “0”state), may indicate a reading time for reading data (e.g., “tR” shownin FIG. 2A), program time for programming data (e.g., “tPRG” shown inFIG. 2B), or a block erase time for erasing block data (e.g., “tBERS”shown in FIG. 2C).

During the timing period “t3”, one or more read status commands 402, 404and 406 may be transmitted to read the status of the flash memorydevice. In some implementations, the first read status command 402 maybe sent after an initial waiting time “t1”. In essence, the initialwaiting time controls when status polling will take place. After thefirst read status command 402 is sent, a second read status command 404may be sent. The second read status command 404 may be sent after afirst interval time “t2” has expired. After the second read statuscommand 404 has been sent, a third read status command 406 may betransmitted after a second interval time “t4”. In some implementations,the first interval time “t2” and the second interval time “t4” may bethe same. In other implementations, the first interval time “t2” and thesecond interval time “t4” may be different.

In the implementations shown above, both the initial waiting time “t1”,the first interval time “t2” and the second interval time “t4” may besupplied by the clock generator of the memory controller 330.Alternatively, the initial waiting time “t1”, the first interval time“t2” and the second interval time “t4” may be supplied by the internalclock of the flash memory device.

One advantage attributable to using a read status command for pollingand controlling when the status read command is issued includes avoidingread incoherency of the internal registers of the flash memory device.This may be crucial for a status read where out of date information mayprovide the wrong indication to a processor or memory controller 330.The processor or the memory controller 330 may poll for program or erasestatus and correctly receive current and updated data by directlyreading the register data stored in the status register 336 a-336 d.

FIG. 5 shows an example process 500 for issuing one or more read statuscommands. Process 500 may be performed, for example, by the solid statedrive 300, the solid state drive 304 or the memory controller 330.However, another apparatus, system, or combination of systems, may beused to perform the process 500.

Process 500 begins with asserting a control signal to one or more memorydevices (502). In some implementations, asserting a control signal mayinclude asserting a read enable, write enable or chip enable (or chipselect) signal to one or more flash memory devices. The flash memorydevices, in some implementations, may include NAND-type memory devices.

Then, an initial wait time may be determined (504). In someimplementations, the initial wait time may include a time period duringwhich a memory controller (e.g., memory controller 330) may wait beforeissuing a command to the flash memory devices (e.g., during a read,program or erase operation).

A first command may be issued based on the initial wait time (506). Insome implementations, the memory controller may issue the first commandafter the initial wait time. In these implementations, the first commandmay be a status check command (e.g., a read status check command or aprogram status check command).

In some implementations, asserting a control signal may includeasserting a read command to the one or more memory devices. In theseimplementations, issuing a first command then may include issuing a readstatus command based the initial wait time.

In other implementations, asserting a control signal may includeasserting a program (or write) command to the one or more memorydevices. In these implementations, issuing a first command then mayinclude issuing a program status command based the initial wait time.

Next, a first interval time associated with the first command may bedetermined (508). The first interval time may be associated with theinterval time between two read status commands. For example, a firstread status command may be sent after the initial wait period. After thefirst read status command is sent, a second read status command may besent to the flash memory device. The second read status command may besent after the first interval time has expired. After the second readstatus command has been sent, a third read status command may betransmitted after a second interval time.

A second command may then be issued based on the first interval time(510). In some implementations, a second interval time associated withthe second command also may be determined as discussed above. The secondinterval time, in these implementations, may be determined with respectto the second command and a third command. Based on the second intervaltime, the third command may be issued.

In some implementations, operations 502-510 may be performed in theorder listed, in parallel (e.g., by the same or a different program orthread executing on one or more processors, substantially or otherwisenon-serially), or in reverse order to achieve desirable results. Inother implementations, operations 502-510 may be performed out of theorder shown. Also, the order in which the operations are performed maydepend, at least in part, on which entity performs the process 500.Operations 502-510 further may be performed by the same or differententities or systems.

Read Cycle Time and Write Cycle Time

Conventional solid state storage devices employ multi-dimensional memoryarray systems to increase performance and maximize capacity. However,conventional solid state systems are not typically adapted to utilizesolid state storage devices of different types in a same system. Forexample, a conventional solid state system cannot utilize both singlelevel cell devices and multi-level cell devices in the same systemefficiently. As an example, if the read/busy out signal “R/B_” is notused and only a single timer is provided for both SLC and MLC, it may bedifficult to find an optimal setting for the single timer which worksgood for both SLC and MLC (e.g., because SLC and MLC have differentoptimal “tR”, “tPROG” and “tBERS” periods). Thus, when a small timer isselected for optimal SLC performance, the timer may not be suitable forachieving maximum MLC performance (e.g., in terms of power). Similarly,if a big timer is used for achieving maximum MLC performance (e.g., toreduce power), SLC status may not be detected in a timely manner, thuscausing performance degradation.

While slower devices such as MLC devices generally cost less and may beused to meet conventional capacity requirement and lower the overallcost of the storage device implementing the MLC devices, MLC devices maynot be used in the same system as the faster devices such as SLC devicesdue to, for example, parameter conflicts. For example, SLC devices andMLC devices often require different manufacturer requirements andspecification for data access (e.g., different timing parameters).

For example, referring back to FIG. 2A, to execute a read operation, theread enable signal (RE_) may be asserted and toggled between logical “1”and logical “0” for a predetermined number of cycles (e.g., when theflash memory device is operating in the data transfer region 204). Asingle cycle may be defined by the period of the read cycle time “tRC”.More specifically, the read cycle time “tRC” may define a reading timeduring which data from the flash memory device may be read.

In some implementations, the read cycle time “tRC” may be about 50 ns(e.g., for MLC devices). More specifically, in the example shown, theread cycle time “tRC” may include a first timing period T1 and a secondtiming period T2. The first timing period T1 and the second timingperiod T2 may define the flash access timing associated with each readcycle time “tRC”. In some implementations, the first timing period T1may span a duration period of 4*T, where T is 160 MHz or about 6.25 ns.In other words, the first timing period T1 may be about 25 ns in length.In these implementations, the second timing period T2 also may span aduration period of 4*T or about 25 ns in length. A first timing periodT1 of about 25 ns and a second timing period T2 of about 25 ns in lengthwould then yield a total read cycle time “tRC” of about 50 ns.

In other implementations, the read cycle time “tRC” may be about 25 ns(e.g., for SLC devices). For example, the first timing period T1 mayspan a duration period of 2*T, where T is 160 MHz or about 6.25 ns. Inother words, the first timing period T1 may be about 12.5 ns in length.In some implementations, the second timing period T2 also may span aduration period of 2*T or about 12.5 ns in length. A first timing periodT1 of about 12.5 ns and a second timing period T2 of about 12.5 ns inlength then yield a total read cycle time “tRC” of about 25 ns.

The read cycle time “tRC” need not be limited to the timing period shownabove, and other read cycle time periods also are contemplated. Forexample, depending on a particular design and application, in someimplementations, the read cycle time “tRC” may be in the range of 20 ns.

In some implementations, the read cycle time “tRC” (and the write cycletime “tWC” as will be discussed below) may be shorter (e.g., faster)than the cycle time associated with the read enable signal (or writeenable signal with respect to the write cycle time “tWC”). In theseimplementations, the solid state drive system 300 may provide an SOCinternal clock to generate both the read cycle time “tRC” and the writecycle time “tWC” as NAND flash I/O interface signals based on the readenable signal and the write enable signal. For example, if the low timeand high time associated with a NAND flash read enable signal are 10 nsand 15 ns respectively, then the internal clock may be 200 Mhz (5 ns).Then, the value for the first timing period T1 may be programmed toallow a 2T cycle (e.g., 5 ns×2=ns) and the value for the second timingperiod T2 may be programmed to allow a 3T cycle (5 ns×3=15n).

Referring to FIG. 2B, to execute a data program operation, the writeenable signal (WE_) may be asserted and toggled between logical “1” andlogical “0” for a predetermined number of cycles (e.g., when the flashmemory device is operating in the command sending region 206). A singlecycle may be defined by the period of the write cycle time “tWC”. Morespecifically, the write cycle time “tWC” may define a writing timeduring which programming data from the flash memory device may bewritten.

In some implementations, the write cycle time “tWC” may be about 50 ns(e.g., for MLC devices). More specifically, in the example shown, theread cycle time “tRC” may include a first timing period T1 and a secondtiming period T2. The first timing period T1 and the second timingperiod T2 may define the flash access timing associated with each writecycle time “tWC”. In some implementations, the first timing period T1may span a duration period of 4*T, where T is 160 MHz or about 6.25 ns.In other words, the first timing period T1 may be about 25 ns in length.In some implementations, the second timing period T2 also may span aduration period of 4*T or about 25 ns in length. A first timing periodT1 of about 25 ns and a second timing period T2 of about 25 ns in lengthwould then yield a total write cycle time “tWC” of about 50 ns.

In other implementations, the write cycle time “tWC” may be about 25 ns(e.g., for SLC devices). For example, the first timing period T1 mayspan a duration period of 2*T, where T is 160 MHz or about 6.25 ns. Inother words, the first timing period T1 may be about 12.5 ns in length.In some implementations, the second timing period T2 also may span aduration period of 2*T or about 12.5 ns in length. A first timing periodT1 of about 12.5 ns and a second timing period T2 of about 12.5 ns inlength then yield a total write cycle time “tWC” of about 25 ns.

Of course, the write cycle time “tWC” is not limited to the timingperiod shown above, and other write cycle time periods also arecontemplated. For example, depending on a particular design andapplication, in some implementations, the write cycle time “tWC” may bein the range of 45 ns.

In general, the read cycle time “tRC” and the write cycle time “tWC” maybe used as timing parameters for determining the overall performance ofthe data transfer rate. By adjusting the read cycle time “tRC” and thewrite cycle time “tWC” appropriately, the interface timing associatedwith the flash memory device may be controlled so that a mixture of SLCand MLC devices may be used. As an example, upon issuing a READ command,the solid state drive system 300 may wait for an internal buffer to beready after a “tR” period as shown in FIG. 2A. Thereafter, data areshifted out from the internal buffer through the NAND interface to thesolid state controller 308. The frequency of shifting then may bespecified by the “tRC” period for a read operation (or by the “tWC”period for a programming operation). As discussed above, the maximumthroughput may be given by “1/tRC” (e.g., a 40 MHz for a “tRC” period=25ns). In other words, minimizing the “tRC” period (or the “tWC” period)allows an increase in bandwidth. Hence, by defining two different timingparameters (e.g., one configured for SLC devices and another configuredfor MLC devices as opposed to utilizing a same logic (timing parameters)to control the timing interface for both SLC and MLC devices),efficiency is significantly improved.

As another example, a solid state drive may utilize a first flash memorydevice with a read cycle time “tRC” of 25 ns and a write cycle time“tWC” of 25 ns, a second flash memory device with a read cycle time“tRC” of 25 ns and a write cycle time “tWC” of 45 ns, a third flashmemory device with a read cycle time “tRC” of 20 ns and a write cycletime “tWC” of 20 ns, and a fourth flash memory device with a read cycletime “tRC” of 50 ns and a write cycle time “tWC” of 50 ns. In someimplementations, because data are not shifted in or out during a blockerase operation, a cycle time is not used for a block erase operation.

FIG. 6 shows an example process 600 for status polling based on a writecycle time and a read cycle time. Process 600 may be performed, forexample, by the solid state drive system 300, the solid state drive 304or the memory controller 330. However, another apparatus, system, orcombination of systems, may be used to perform the process 600.

Process 600 begins with controlling a plurality of memory devicesincluding a first group of memory devices and a second group of memorydevices (602). In some implementations, the first group of memorydevices may include single-level cell devices, while the second group ofmemory devices may include multi-level cell devices. In otherimplementations, the first group of memory devices may includemulti-level cell devices, while the second group of memory devices mayinclude single-level cell devices.

Next, a first cycle time may be determined (604). In someimplementations, determining a first cycle time may include determininga first cycle time associated with a first group of memory devices. Inthese implementations, determining a first cycle time associated withthe first group of memory devices may include determining a first timingparameter (e.g., the “tRC” period shown in FIG. 2A) and a second timingparameter (e.g., the “tWC” period shown in FIG. 2B), the first timingparameter and the second timing parameter being associated with a datatransfer rate of the first group of memory devices (e.g., single-levelcell devices). In some implementations, the first cycle time may be aread cycle time associated with a read operation during which data fromat least one of the memory deices may be read. In other implementations,the first cycle time may be a program cycle time associated with aprogram operation during which data may be programmed into at least oneof the memory devices.

Thereafter, a write command may be issued based on the first cycle time(606). In some implementations, the first command may be issued to thefirst group of memory devices based on the first cycle time. Forexample, a write enable signal (WE_) with a rising and falling edgecorresponding to the first cycle time may be issued. The write enablesignal (WE_) may toggle between logical “0” and logical “1” while awrite operation is being processed.

After issuing a write command, a second cycle time is determined (608).In some implementations, determining a second cycle time may includedetermining a second cycle time associated with a second group of memorydevices. The second group of memory devices may be different from thefirst group of memory devices. For example, the first group of memorydevices may include single-level cell devices, while the second group ofmemory devices may include multi-level cell devices. In someimplementations, determining a second cycle time may include determiningthe second cycle time independent of the first cycle time. For example,the “tRC” or “tWC” period associated with single-level cell devices maybe determined separate from those associated with multi-level celldevices. In some implementations, the “tRC” or “tWC” period may be usedto maximize a data transfer rate of a corresponding memory device.

In some implementations, a control signal (e.g., a read enable signal, awrite enable signal or a chip enable signal) may be asserted to one ofthe first or second group of memory devices for a predetermined numberof cycles. In these implementations, the predetermined number of cyclesmay include a first cycle associated with the first cycle time, thefirst cycle including a first timing period (e.g., the first timingperiod “T1” shown in FIGS. 2A and 2B) and a second timing period (e.g.,the second timing period “T2” shown in FIGS. 2A and 2B). In theseimplementations, the first timing period and the second timing period ofthe first cycle may include a same or different duration.

In some implementations, the predetermined number of cycles may includea second cycle associated with the second cycle time, the second cycleincluding a first timing period (e.g., the first timing period “T1”shown in FIGS. 2A and 2B) and a second timing period (e.g., the secondtiming period “T2” shown in FIGS. 2A and 2B). In these implementations,the first timing period and the second timing period of the second cyclemay include a same or different duration.

In some implementations, a wait period (e.g., the “tR” period shown inFIG. 2A) may be determined. The wait period may function as a wait timeduring which no command (e.g., read status or write status command) maybe issued to either the first group of memory devices or the secondgroup of memory devices. Thereafter, the first command or the secondcommand may be issued to its corresponding group.

With the second cycle time determined, a second command may be issuedbased on the second cycle time (610). For example, a read enable signal(RE_) with a rising and falling edge corresponding to the second cycletime may be issued. The read enable signal (RE_) may toggle betweenlogical “0” and logical “1” while a read operation is being processed.

In some implementations, operations 602-610 may be performed in theorder listed, in parallel (e.g., by the same or a different program orthread executing on one or more processors, substantially or otherwisenon-serially), or in reverse order to achieve desirable results. Inother implementations, operations 602-610 may be performed out of theorder shown. Also, the order in which the operations are performed maydepend, at least in part, on which entity performs the process 600.Operations 602-610 further may be performed by the same or differententities or systems.

Example Implementations of Hard Disk Drive

FIGS. 7-13 show various example implementations of the described systemsand techniques. Referring now to FIG. 7, the described systems andtechniques can be implemented in a hard disk drive (HDD) 700. Thedescribed systems and techniques may be implemented in either or bothsignal processing and/or control circuits, which are generallyidentified in FIG. 7 as 702. In some implementations, the signalprocessing and/or control circuit 702 and/or other circuits (not shown)in the HDD 700 may process data, perform coding and/or encryption,perform calculations, and/or format data that is output to and/orreceived from a magnetic storage medium 704.

The HDD 700 may communicate with a host device (not shown) such as acomputer, mobile computing devices such as personal digital assistants,cellular phones, media or MP3 players and the like, and/or other devicesvia one or more wired or wireless communication links 706. The HDD 700may be connected to memory 708 such as random access memory (FAM), lowlatency nonvolatile memory such as flash memory, read only memory (ROM)and/or other suitable electronic data storage.

Referring now to FIG. 8, the described systems and techniques can beimplemented in a digital versatile disc (DVD) drive 800. The describedsystems and techniques may be implemented in either or both signalprocessing and/or control circuits, which are generally identified inFIG. 8 as 802, and/or mass data storage 804 of the DVD drive 800. Thesignal processing and/or control circuit 802 and/or other circuits (notshown) in the DVD drive 800 may process data, perform coding and/orencryption, perform calculations, and/or format data that is read fromand/or data written to an optical storage medium 806. In someimplementations, the signal processing and/or control circuit 802 and/orother circuits (not shown) in the DVD drive 800 can also perform otherfunctions such as encoding and/or decoding and/or any other signalprocessing functions associated with a DVD drive.

The DVD drive 800 may communicate with an output device (not shown) suchas a computer, television or other device via one or more wired orwireless communication links 810. The DVD drive 800 may communicate withmass data storage 804 that stores data in a nonvolatile manner. The massdata storage 804 may include a hard disk drive (HDD). The HDD may havethe configuration shown in FIG. 7. The HDD may be a mini HDD thatincludes one or more platters having a diameter that is smaller thanapproximately 1.8″. The DVD drive 800 may be connected to memory 808such as RAM, ROM, low latency nonvolatile memory such as flash memoryand/or other suitable electronic data storage.

Referring now to FIG. 9, the described systems and techniques can beimplemented in a high definition television (HDTV) 900. The describedsystems and techniques may be implemented in either or both signalprocessing and/or control circuits, which are generally identified inFIG. 9 as 902, a WLAN interface 906 and/or mass data storage 910 of theHDTV 900. The HDTV 900 receives HDTV input signals in either a wired orwireless format and generates HDTV output signals for a display 904. Insome implementations, signal processing circuit and/or control circuit902 and/or other circuits (not shown) of the HDTV 900 may process data,perform coding and/or encryption, perform calculations, format dataand/or perform any other type of HDTV processing that may be required.

The HDTV 900 may communicate with mass data storage 910 that stores datain a nonvolatile manner such as optical and/or magnetic storage devices.At least one HDD may have the configuration shown in FIG. 7 and/or atleast one DVD drive may have the configuration shown in FIG. 8. The HDDmay be a mini HDD that includes one or more platters having a diameterthat is smaller than approximately 1.8″ The HDTV 900 may be connected tomemory 908 such as RAM, ROM, low latency nonvolatile memory such asflash memory and/or other suitable electronic data storage. The HDTV 900also may support connections with a WLAN via a WLAN network interface906.

Referring now to FIG. 10, the described systems and techniques can beimplemented in a cellular phone 1000 that may include a cellular antenna1002. The described systems and techniques may be implemented in eitheror both signal processing and/or control circuits, which are generallyidentified in FIG. 10 as 1004, a WLAN interface 1010 and/or mass datastorage 1006 of the cellular phone 1000. In some implementations, thecellular phone 1000 includes a microphone 1012, an audio output 1014such as a speaker and/or audio output jack, a display 1016 and/or aninput device 1018 such as a keypad, pointing device, voice actuationand/or other input device. The signal processing and/or control circuits1004 and/or other circuits (not shown) in the cellular phone 1000 mayprocess data, perform coding and/or encryption, perform calculations,format data and/or perform other cellular phone functions.

The cellular phone 1000 may communicate with mass data storage 1006 thatstores data in a nonvolatile manner such as optical and/or magneticstorage devices for example hard disk drives HDD and/or DVDs. At leastone HDD may have the configuration shown in FIG. 7 and/or at least oneDVD drive may have the configuration shown in FIG. 8. The HDD may be amini HDD that includes one or more platters having a diameter that issmaller than approximately 1.8″The cellular phone 1000 may be connectedto memory 1008 such as RAM, ROM, low latency nonvolatile memory such asflash memory and/or other suitable electronic data storage. The cellularphone 1000 also may support connections with a WLAN via a WLAN networkinterface 1010.

Referring now to FIG. 11, the described systems and techniques can beimplemented in a set top box 1100. The described systems and techniquesmay be implemented in either or both signal processing and/or controlcircuits, which are generally identified in FIG. 11 as 1102, a WLANinterface 1108 and/or mass data storage 1104 of the set top box 1100.The set top box 1100 receives signals from a source 1112 such as abroadband source and outputs standard and/or high definition audio/videosignals suitable for a display 1110 such as a television and/or monitorand/or other video and/or audio output devices. The signal processingand/or control circuits 1102 and/or other circuits (not shown) of theset top box 1100 may process data, perform coding and/or encryption,perform calculations, format data and/or perform any other set top boxfunction.

The set top box 1100 may communicate with mass data storage 1104 thatstores data in a nonvolatile manner. The mass data storage 1104 mayinclude optical and/or magnetic storage devices for example hard diskdrives HDD and/or DVDs. At least one HDD may have the configurationshown in FIG. 7 and/or at least one DVD may have the configuration shownin FIG. 8. The HDD may be a mini HDD that includes one or more plattershaving a diameter that is smaller than approximately 1.8″The set top box1100 may be connected to memory 1106 such as RAM, ROM, low latencynonvolatile memory such as flash memory and/or other suitable electronicdata storage. The set top box 1100 also may support connections with aWLAN via a WLAN network interface 1108.

Referring now to FIG. 12, the described systems and techniques can beimplemented in a media player 1200. The described systems and techniquesmay be implemented in either or both signal processing and/or controlcircuits, which are generally identified in FIG. 12 as 1202, a WLANinterface 1208 and/or mass data storage 1204 of the media player 1200.In some implementations, the media player 1200 includes a display 1212and/or a user input 1214 such as a keypad, touchpad and the like. Insome implementations, the media player 1200 may employ a graphical userinterface (GUI) that typically employs menus, drop down menus, iconsand/or a point-and-click interface via the display 1212 and/or userinput 1214. The media player 1200 further includes an audio output 1210such as a speaker and/or audio output jack. The signal processing and/orcontrol circuits 1202 and/or other circuits (not shown) of the mediaplayer 1200 may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other media playerfunction.

The media player 1200 may communicate with mass data storage 1204 thatstores data such as compressed audio and/or video content in anonvolatile manner. In some implementations, the compressed audio filesinclude files that are compliant with MP3 (Moving Picture experts groupaudio layer 3) format or other suitable compressed audio and/or videoformats. The mass data storage may include optical and/or magneticstorage devices for example hard disk drives HDD and/or DVDs. At leastone HDD may have the configuration shown in FIG. 7 and/or at least oneDVD may have the configuration shown in FIG. 8. The HDD may be a miniHDD that includes one or more platters having a diameter that is smallerthan approximately 1.8″The media player 1200 may be connected to memory1206 such as RAM, ROM, low latency nonvolatile memory such as flashmemory and/or other suitable electronic data storage. The media player1200 also may support connections with a WLAN via a WLAN networkinterface 1208. Still other implementations in addition to thosedescribed above are contemplated.

A few embodiments have been described in detail above, and variousmodifications are possible. The disclosed subject matter, including thefunctional operations described in this specification, can beimplemented in electronic circuitry, computer hardware, firmware,software, or in combinations of them, such as the structural meansdisclosed in this specification and structural equivalents thereof,including potentially a program operable to cause one or more dataprocessing apparatus to perform the operations described (such as aprogram encoded in a computer-readable medium, which can be a memorydevice, a storage device, a machine-readable storage substrate, or otherphysical, machine-readable medium, or a combination of one or more ofthem).

The term “data processing apparatus” encompasses all apparatus, devices,and machines for processing data, including by way of example aprogrammable processor, a computer, or multiple processors or computers.The apparatus can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

A program (also known as a computer program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, or declarative orprocedural languages, and it can be deployed in any form, including as astand alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A program does notnecessarily correspond to a file in a file system. A program can bestored in a portion of a file that holds other programs or data (e.g.,one or more scripts stored in a markup language document), in a singlefile dedicated to the program in question, or in multiple coordinatedfiles (e.g., files that store one or more modules, sub programs, orportions of code). A program can be deployed to be executed on onecomputer or on multiple computers that are located at one site ordistributed across multiple sites and interconnected by a communicationnetwork.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of what may be claimed, but ratheras descriptions of features that may be specific to particularembodiments. Certain features that are described in this specificationin the context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the embodiments described above should not be understoodas requiring such separation in all embodiments.

What is claimed is:
 1. A method comprising: controlling a plurality ofmemory devices including a first group of memory devices and a secondgroup of memory devices; determining a first period associated with thefirst group of memory devices; issuing a first command to the firstgroup of memory devices based on the first period; determining a secondperiod associated with the second group of memory devices; and issuing asecond command to the second group of memory devices based on the secondperiod.
 2. The method of claim 1, where determining a second periodassociated with the second group of memory devices includes determiningthe second period independent of the first period.
 3. The method ofclaim 1, where determining a first period associated with the firstgroup of memory devices includes: determining a first timing parameterand a second timing parameter, the first timing parameter and the secondtiming parameter being associated with a data transfer rate of the firstgroup of memory devices.
 4. The method of claim 1, where determining asecond period associated with the second group of memory devicesincludes: determining a first timing parameter and a second timingparameter, the first timing parameter and the second timing parameterbeing associated with a data transfer rate of the second group of memorydevices.
 5. The method of claim 1, where controlling a plurality ofmemory devices includes: asserting a control signal to the first groupof memory devices for a predetermined number of cycles including a firstcycle associated with the first period, the first cycle including afirst timing period and a second timing period.
 6. The method of claim5, where the first timing period and the second timing period of thefirst cycle include a same duration.
 7. The method of claim 5, where thefirst timing period and the second timing period of the first cycleinclude a different duration.
 8. The method of claim 1, wherecontrolling a plurality of memory devices includes: asserting a controlsignal to the second group of memory devices for a predetermined numberof cycles including a second cycle associated with the second period,the second cycle including a first timing period and a second timingperiod.
 9. The method of claim 8, where the first timing period and thesecond timing period of the second cycle include a same duration. 10.The method of claim 8, where the first timing period and the secondtiming period of the second cycle include a different duration.
 11. Themethod of claim 1, where determining a first period includes determininga read period during which data from at least one of the memory devicesis read, or a program period during which data is programmed into atleast one of the memory devices.
 12. The method of claim 1, wherecontrolling a plurality of memory devices includes determining a waitperiod.
 13. The method of claim 12, where issuing a first commandincludes issuing the first command after the wait period.
 14. The methodof claim 12, where issuing a second command includes issuing the secondcommand after the wait period.